http://www.youtube.com/watch?v=FV_6ZE4lOQs
http://www.tp-link.com/en/support/calculator/#3

i dont advice Bridge mode,
1-5210s will work at 50% of its capacity
2-you will have to use WEP security, do you really want to use WEP today

I want to establish a bridge from building A to building B

that means you are in urban area,
1-do you really want to use 2.4Ghz crowded band
2-better use 5Ghz band (if you are able, due to country regulations) if so use 7510
3-dont forget the link will be in 5Ghz and you will need to add at point B any router, like the 740 or 741 as router or as AP (this apply to 5210 too)
4-in both cases 2.4 or 6Ghz use
building A as AP mode http://www.tp-link.com/en/article/?faqid=393
and building as Client mode http://www.tp-link.com/en/article/?faqid=318
and if you decide for 7510 read http://www.tp-link.com/en/article/?faqid=462